The present invention relates to a plant for producing pressure die-cast or injection moulded articles using salt cores.
As is known, pressure die-cast or injection moulded articles are produced by injecting a material in liquid formxe2x80x94either a metal (for example aluminium) or a plastic (for example polyamides)xe2x80x94into a mould bearing a negative impression of the desired article. It is common practice, moreover, to place one or more filler cores inside the mould so as to produce articles with cavities and/or apertures of a particular shape.
For some time now, the problems connected with the need to extract the filler cores from within the article once the material injected into the mould has solidified have led those working in the field to examine the possibility of making the filler cores by compressing salt grains (for example sodium chloride grains) inside moulds bearing a negative impression of the core shape. Indeed, such a solution would enable the filler cores to be removed from within the article simply by washing the said article with a liquid solvent (for example water) capable of dissolving the salt grains, and would also make it possible to adopt design solutions which could not otherwise be used with conventional techniques.
At present, however, the use of salt filler cores is very much limited by the difficulty in obtaining sufficient quantities of salt grains having suitable morphological characteristics to satisfyxe2x80x94at an industrially acceptable costxe2x80x94the requirements of a plant for producing pressure die-cast or injection moulded articles.
Through experimentation, it has been observed that, in order to withstand the stresses generated during injection of the material in a liquid state into the mould, the salt filler cores need to be extremely compact and, consequently, the shape and particle size of the salt grains used to produce these cores have to be such as to ensure that the maximum possible density is achieved once the salt grains have been compressed inside the moulds for producing the cores.
At present, salt grains that are suitable for producing salt filler cores are only obtained after a lengthy and expensive process involving, firstly, a grinding stage in which generic salt agglomerates are fed into grinders from which salt grains of varying particle size are obtained and, subsequently, a grading stage in which the salt grains produced by the grinders are conveyed into screening machines capable of separating from the stream of salt grains those salt grains that are of a suitable size for producing the salt cores referred to above.
The production process described above has the great disadvantage of giving a low specific yield; consequently, in order to ensure that enough salt grains are produced to satisfy the needs of a plant for producing pressure die-cast or injection moulded articles, the number of grinders and screening machines needed would be such as to make construction of the plant unfeasible on account of the excessive costs involved. Furthermore, the salt grains obtained using the production process described above have many sharp edges which do not particularly lend themselves to achieving high levels of compaction.
The object of the present invention is, therefore, to provide a plant for producing pressure die-cast or injection moulded articles using salt filler cores which does not have the disadvantages listed above.
According to the present invention, a plant is provided for producing pressure die-cast or injection moulded articles using salt cores, characterized in that it comprises a unit for producing salt grains having a shape and particle size suitable for producing salt filler cores; a press designed to make at least one said salt filler core by compacting a given quantity of salt grains; and a pressure die-casting machine designed to produce the said pressure die-cast or injection moulded articles by injecting a material in the liquid state into a mould containing at least one salt filler core produced by the said press; the said unit for producing salt grains being designed to atomize a saline solution into a plurality of drops and to cause the salt contained in each drop to solidify into a corresponding salt grain.